This thesis investigates the profession of conference interpreting, adopting a comparative analysis of the profession as a social practice in the United Kingdom and Japan. Conference interpreting is a specialised, cognitively challenging oral language translation service, used in high-level settings such as diplomacy, business, politics, and supranational institutions. Interpreters translate a speaker's message from one language to another to their clients, either simultaneously, whilst the speaker speaks, or consecutively, after the speaker has spoken. Interpreting has a peculiar organisation as a profession: Performing as the voices of other individuals, interpreters are bound by their code of conduct to work by collaborating in teams, observe strict professional rules, and provide seamless communication as if they were invisible in the interaction. This organisation helps interpreters to avoid or hide failure which, when it occurs, happens in âreal-timeâ and publicly under the eyes of users and colleagues, with potentially damaging consequences for professional reputation and status. Drawing upon a practice theories approach, this thesis analyses interpreting as an integrative professional practice, focusing on its organisation and on the concrete practices of interpreters to understand how their expertise and professional status are organised, and tied to local socio-cultural specificities of the Japanese and British markets for linguistic services. Previous research has explored interpreting as a discourse process, as a social activity, and as a profession, but has failed to address how the distinctive features of interpreting as a social practice affect questions of expertise, failure, and status relations in the profession. This thesis argues that we can only resolve these gaps by looking at interpretersâ practical accomplishments and professional struggles as the result of the collective organisation of the practice. Hence, the thesis addresses these questions: How does the distinctive nature of conference interpreting as an integrative social practice of mediated communication affect the organisation and performance of interpretersâ expertise? How does the social organisation of interpreting expertise affect how the practice is understood by clients, and impact on interpretersâ professional status, and their social relations on the job? This thesis argues that the collectively steered, constitutive features of interpreting have particular implications for how the expertise of interpreters and its aspects are reproduced and organised in performances. In addition, this thesis argues that such distinctive features relate to how expertise is produced, organised, and operationalised in performances and have particular implications for how interpretersâ expertise is understood by clients. The thesis is based on qualitative ethnographic âinsiderâ research on the interpreting profession in the UK and in Japan, conducted through interviews, participant observations, and analysis of documents and material artefacts, a combination undertaken to account for the macro and micro dimensions of the practice. My thesis shows that interpreting is a professional practice characterised by power struggles and the âinvisibilisationâ of interpretersâ expertise which arise out of the particular organisation of the practice. The social organisation of the practice establishes expertise in interpreting as the âinvisibilisationâ of the interpreter in a seamless âflowâ of successful communication, with the interpreterâs role only becoming âvisibleâ to clients in communication breakdown and failure. Therefore, interpreters are âembedded strangersâ in their own professional practice. However, this creates tensions for interpreters around the management of failure, the joint nature of success or failure in teams, and the display and recognition of expertise. Despite codified rules of practice which exert a strong normative force, interpreters often bend the rules in their favour to cover their failures and enhance their successful performances. Because of the invisibilised nature of their expertise, interpreters struggle to maintain their professional status with clients and wider lay society. This causes precarious relationships with colleagues, and competitive power struggles in order to insulate themselves from team-membersâ failures and also to increase the visibility of their own expertise in the eyes of clients. The thesis explores the expertise, failures, and power struggles of interpreters by analysing how they emerge from the specificities of the social organisation of the practice, offering a comparative lens to understand established practices as tied to local contexts.